1. Field of the Invention
This invention relates to an internal combustion engine for vehicles, and more particularly to a breather structure for an internal combustion engine.
2. Description of the Background Art
Japanese Patent Laid-Open No. Sho 61-160665, which will be explained hereinafter in more detail with reference to FIG. 11, shows a major portion of an exemplary breather structure of a crankcase or a transmission case of an internal combustion engine. A transmission case 02 is located at the rear of a belt-drive case 01 in a unit-swing internal combustion engine.
A breather chamber 03 is formed in the upper part of the transmission case 02. A breather pipe 05 is longitudinally and horizontally inserted in a through hole in a partition wall 03a of the breather chamber 03 through a grommet 04.
The breather pipe 05, whose one end is inserted in the breather chamber 03 is bent downward in the belt-drive case 01, extends vertically through the lower wall of the belt-drive case 01 via a grommet 06 and opens at a lower end out to the atmosphere.
Another arrangement in the background art includes a breather tube that is extended directly outside from the transmission case with the forward end of the tube inserted into an air cleaner box to release the air.
However, the examples described above have the following drawbacks. Since the open end of the breather pipe 05 is open to the atmosphere at the lower part of the vehicle, there is a risk of the entrance of dust and debris, and the subsequent attachment of dust at the outlet depending on the layout. This can impair appearance. Further, the breather pipe 05, having its open end on the underside of the vehicle, has an unfavorable, increased length.
In the latter example, when the air cleaner box is mounted on the vehicle body frame, the belt-drive case is likely to oscillate. Therefore, it becomes necessary to increase the length of the breather tube to absorb these oscillations and/or to provide a special cleaner box for the belt-drive case.
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.
In view of the above-described drawbacks associated with the prior art, it is an object of this invention to provide a breather structure for an internal combustion engine of a vehicle having a simplified construction.
It is a further object of this invention to provide a breather structure that can prevent the entry/attachment of dusts into/onto a breather by using a relatively short breather passage.
These and other objects of the present invention are accomplished by a breather structure for a power unit for vehicles, the breather structure comprising a body cover having an outer side, the body cover covering the power unit; an outer cover mounted to the outer side; a sound absorbing material layer interposed between an inner surface of the outer cover and the body cover for noise suppression, and a breather assembly having an outlet provided in the power unit, the outlet of the breather provided in the power unit and opening in the sound absorbing material.
Since the breather outlet opens in the sound absorbing material interposed between the body cover covering the power unit and the outer cover located on the outside thereof, entry of dusts at the breather outlet and attachment of the dusts on the outlet can be prevented. Therefore no adverse effect will be given to the appearance.
Since it is sufficient to direct the breather outlet toward the sound absorbing material, the breather of a simple structure having a high degree of freedom of layout can be designed as short as possible.
These and other objects are further accomplished by a power unit for vehicles comprising a case enclosing a crankcase of an internal combustion engine and a transmission chamber of the power unit; a cover unit covering the case, the cover unit including an inner cover, an outer front cover, and an outer rear cover covering the inner cover; a space formed between the outer rear cover and the inner cover; a sound absorbing material layer interposed within the space for noise suppression; a transmission cover and a breather chamber; and a connecting pipe fitted through a peripheral wall of the transmission cover, and a lower end of the connecting pipe communicating the breather chamber with an outside of the transmission case via an upper end of the connecting pipe.
Furthermore, since the breather pipe has a horizontal portion of a specific length, the oil will not be forced out by up-down oscillation of the transmission case mounted on the driven pulley side of the belt-drive vehicle.
The unit-swing internal combustion engine is also provided with a transmission case on the driven pulley side of a belt-drive vehicle.
These and other objects are further accomplished by a breather structure for a power unit for vehicles having a belt-drive chamber with an air-cooled structure, the breather structure comprising a body cover having an outer side, the body cover covering the power unit; an outer cover mounted to the outer side; a sound absorbing material layer interposed between an inner surface of the outer cover and the body cover for noise suppression, a breather assembly on a transmission case mounted on a driven pulley side of a belt drive transmission of the power unit, an outlet of the breather assembly opening in the sound absorbing material and formed at a cooled-air outlet port of the belt-drive chamber.
Since the breather outlet opens in the sound absorbing material, dusts can be prevented from entering, and holding onto the breather outlet. Furthermore, oil content discharged out of the outlet of the breather extended from the transmission case is adsorbed by the sound absorbing material. However, because the breather outlet is located at the cooled air outlet of the belt-drive chamber, the sound absorbing material that has adsorbed the oil content is dried with cooled air that is warm air, and therefore can keep its adsorbing performance for a prolonged period of time.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.